26,752 research outputs found
Singular Vortex in Narrow Cylinders of Superfluid 3He-A Phase
Motivated by the on-going rotating cryostat experiments in ISSP, Univ. of
Tokyo, we explore the textures and vortices in superfluid 3He-A phase confined
in narrow cylinders, whose radii are R=50mum and 115mum. The calculations are
based on the Ginzburg-Landau (GL) framework, which fully takes into account the
orbital (l-vector) and spin (d-vector) degrees of freedom for chiral p-wave
pairing superfluid. The GL free energy functional is solved numerically by
using best known GL parameters appropriate for the actual experimental
situations at P=3.2MPa and H=21.6mT. We identify the ground state l-vector
configuration as radial disgyration (RD) texture with the polar core both at
rest and low rotations and associated d-vector textures for both narrow
cylinder systems under high magnetic fields. The RD which has a singularity at
center, changes into Mermin-Ho texture above the critical rotation speed which
is determined precisely, providing an experimental check for own proposal.Comment: 22 pages, 12 figure
Interactive Vegetation Rendering with Slicing and Blending
Detailed and interactive 3D rendering of vegetation is one of the challenges of traditional polygon-oriented computer graphics, due to large geometric complexity even of simple plants. In this paper we introduce a simplified image-based rendering approach based solely on alpha-blended textured polygons. The simplification is based on the limitations of human perception of complex geometry. Our approach renders dozens of detailed trees in real-time with off-the-shelf hardware, while providing significantly improved image quality over existing real-time techniques. The method is based on using ordinary mesh-based rendering for the solid parts of a tree, its trunk and limbs. The sparse parts of a tree, its twigs and leaves, are instead represented with a set of slices, an image-based representation. A slice is a planar layer, represented with an ordinary alpha or color-keyed texture; a set of parallel slices is a slicing. Rendering from an arbitrary viewpoint in a 360 degree circle around the center of a tree is achieved by blending between the nearest two slicings. In our implementation, only 6 slicings with 5 slices each are sufficient to visualize a tree for a moving or stationary observer with the perceptually similar quality as the original model
Helical spin textures in dipolar Bose-Einstein condensates
We numerically study elongated helical spin textures in ferromagnetic spin-1
Bose-Einstein condensates subject to dipolar interparticle forces. Stationary
states of the Gross-Pitaevskii equation are solved and analyzed for various
values of the helical wave vector and dipolar coupling strength. We find two
helical spin textures which differ by the nature of their topological defects.
The spin structure hosting a pair of Mermin-Ho vortices with opposite mass
flows and aligned spin currents is stabilized for a nonzero value of the
helical wave vector.Comment: 7 pages, 6 figure
Spin textures in slowly rotating Bose-Einstein Condensates
Slowly rotating spin-1 Bose-Einstein condensates are studied through a
variational approach based upon lowest Landau level calculus. The author finds
that in a gas with ferromagnetic interactions, such as Rb, angular
momentum is predominantly carried by clusters of two different types of
skyrmion textures in the spin-vector order parameter. Conversely, in a gas with
antiferromagnetic interactions, such as Na, angular momentum is carried
by -disclinations in the nematic order parameter which arises from spin
fluctuations. For experimentally relevant parameters, the cores of these
-disclinations are ferromagnetic, and can be imaged with polarized light.Comment: 14 pages, 12 low resolution bitmapped figures, RevTeX4. High
resolution figures available from author. Suplementary movies available from
autho
A Generative Model of Natural Texture Surrogates
Natural images can be viewed as patchworks of different textures, where the
local image statistics is roughly stationary within a small neighborhood but
otherwise varies from region to region. In order to model this variability, we
first applied the parametric texture algorithm of Portilla and Simoncelli to
image patches of 64X64 pixels in a large database of natural images such that
each image patch is then described by 655 texture parameters which specify
certain statistics, such as variances and covariances of wavelet coefficients
or coefficient magnitudes within that patch.
To model the statistics of these texture parameters, we then developed
suitable nonlinear transformations of the parameters that allowed us to fit
their joint statistics with a multivariate Gaussian distribution. We find that
the first 200 principal components contain more than 99% of the variance and
are sufficient to generate textures that are perceptually extremely close to
those generated with all 655 components. We demonstrate the usefulness of the
model in several ways: (1) We sample ensembles of texture patches that can be
directly compared to samples of patches from the natural image database and can
to a high degree reproduce their perceptual appearance. (2) We further
developed an image compression algorithm which generates surprisingly accurate
images at bit rates as low as 0.14 bits/pixel. Finally, (3) We demonstrate how
our approach can be used for an efficient and objective evaluation of samples
generated with probabilistic models of natural images.Comment: 34 pages, 9 figure
Chiral spin currents and spectroscopically accessible single merons in quantum dots
We provide unambiguous theoretical evidence for the formation of
correlation-induced isolated merons in rotationally-symmetric quantum dots. Our
calculations rely on neither the lowest-Landau-level approximation, nor on the
maximum-density-droplet approximation, nor on the existence of a spin-polarized
state. For experimentally accessible system parameters, unbound merons condense
in the ground state at magnetic fields as low as T and for as few
as N = 3 confined fermions. The four-fold degenerate ground-state at
corresponds to four orthogonal merons characterized by their
topological chirality and charge . This degeneracy is lifted by the
Rashba and Dresselhaus spin-orbit interaction, which we include perturbatively,
yielding spectroscopic accessibility to individual merons. We further derive a
closed-form expression for the topological chirality in the form of a chiral
spin current and use it to both characterize our states and predict the
existence of other topological textures in other regions of phase space, for
example, at N=5. Finally, we compare the spin textures of our numerically exact
meron states to ansatz wave-functions of merons in quantum Hall droplets and
find that the ansatz qualitatively describes the meron states.Comment: 4 pages, 5 figures; minor title change, typos fixe
3D Textured Model Encryption via 3D Lu Chaotic Mapping
In the coming Virtual/Augmented Reality (VR/AR) era, 3D contents will be
popularized just as images and videos today. The security and privacy of these
3D contents should be taken into consideration. 3D contents contain surface
models and solid models. The surface models include point clouds, meshes and
textured models. Previous work mainly focus on encryption of solid models,
point clouds and meshes. This work focuses on the most complicated 3D textured
model. We propose a 3D Lu chaotic mapping based encryption method of 3D
textured model. We encrypt the vertexes, the polygons and the textures of 3D
models separately using the 3D Lu chaotic mapping. Then the encrypted vertices,
edges and texture maps are composited together to form the final encrypted 3D
textured model. The experimental results reveal that our method can encrypt and
decrypt 3D textured models correctly. In addition, our method can resistant
several attacks such as brute-force attack and statistic attack.Comment: 13 pages, 7 figures, under review of SCI
Spin textures in condensates with large dipole moments
We have solved numerically the ground states of a Bose-Einstein condensate in
the presence of dipolar interparticle forces using a semiclassical approach.
Our motivation is to model, in particular, the spontaneous spin textures
emerging in quantum gases with large dipole moments, such as 52Cr or Dy
condensates, or ultracold gases consisting of polar molecules. For a
pancake-shaped harmonic (optical) potential, we present the ground state phase
diagram spanned by the strength of the nonlinear coupling and dipolar
interactions. In an elongated harmonic potential, we observe a novel helical
spin texture. The textures calculated according to the semiclassical model in
the absence of external polarizing fields are predominantly analogous to
previously reported results for a ferromagnetic F = 1 spinor Bose-Einstein
condensate, suggesting that the spin textures arising from the dipolar forces
are largely independent of the value of the quantum number F or the origin of
the dipolar interactions.Comment: 9 pages, 6 figure
Designing Electron Spin Textures and Spin Interferometers by Shape Deformations
We demonstrate that the spin orientation of an electron propagating in a
one-dimensional nanostructure with Rashba spin-orbit (SO) coupling can be
manipulated on demand by changing the geometry of the nanosystem. Shape
deformations that result in a non-uniform curvature give rise to complex
three-dimensional spin textures in space. We employ the paradigmatic example of
an elliptically deformed quantum ring to unveil the way to get an
all-geometrical and all-electrical control of the spin orientation. The
resulting spin textures exhibit a tunable topological character with windings
around the radial and the out-of-plane directions. We show that these
topologically non trivial spin patterns affect the spin interference effect in
the deformed ring, thereby resulting in different geometry-driven ballistic
electronic transport behaviors. Our results establish a deep connection between
electronic spin textures, spin transport and the nanoscale shape of the system.Comment: 8 pages, 4 figure
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